Method for modifying the water permeability of a subterranean formation

ABSTRACT

The invention relates to a method for modifying the water permeability of a subterranean formation, comprising at least the following steps:Preparing an injection fluid from a dispersion of a hydrophilic phase in a lipophilic phase, with water or brine, the dispersion comprising:a hydrophilic phase comprising at least one cross-linked (co)polymer PR,a lipophilic phase,at least one interface polymer composed of at least one monomer of formula (I):Injecting the injection fluid into the subterranean formation,said cross-linked (co)polymer PR forming a hydrogel in the presence of water.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.17/422,840, which published as US 2022-0081604 A1 on Mar. 17, 2022,which is a national stage filing under section 371 of InternationalApplication No. PCT/FR2020/050134 filed on Jan. 29, 2020, and publishedon Aug. 6, 2020 as WO 2020/157429, which claims priority to FrenchApplication No. 1901021, filed on Feb. 1, 2019. The entire contents ofWO 2020/157429 and US 2022-0081604 A1 are hereby incorporated herein byreference.

FIELD OF THE INVENTION

This invention is in the field of recovering oil and gas from asubterranean formation. More particularly, the invention relates to amethod for modifying the water permeability of a subterranean formation,comprising injecting, into the subterranean formation, an injectionfluid comprising at least one (co)polymer encapsulated in a shell.

PRIOR ART

Injecting viscous or gelled polymer solutions into subterraneanformations has been a very widespread practice for many years in orderto improve hydrocarbon (oil and gas) recovery. These polymer solutionsare used in particular to reduce or eliminate the water permeability ofa zone or a part of a subterranean formation.

Formations sometimes have zones of interest containing hydrocarbons butwith strong permeability contrasts or different water volume fractions.In such cases, and when additional pressure is applied in thesubterranean formation with the injection of water in order to producehydrocarbons, the injected water finds the path offering the leastresistance to its propagation, namely the relative permeability mostfavourable to water, to reach the production wells rapidly; in otherwords, it passes through zones having a high volume fraction of waterand/or having a high permeability, thus flowing past other zones rich inhydrocarbons that are less favourable to its propagation, withoutpushing them towards the production wells.

Polymer solutions are injected into such high-permeability and/or highwater-content zones to replace the existing fluids and reduce theirwater permeability by virtue of their high viscosity. Once in theirgelled form, these polymer solutions are used to divert the flow ofwater or gas towards the less permeable zones by permanently blockingthe high-permeability zones. The blocking of certain zones may indeedprove necessary, since they may result in water inflows which seriouslyhinder hydrocarbon recovery.

However, during the injection of the polymers into the subterraneanformation, the polymer solutions undergo mechanical and chemicaldegradation. Mechanical degradation is due to high shear stresses andelongational flows, especially in the initial injection unit, nozzlesand pumps, constrictions in reservoirs and around wells. Chemicaldegradation is mainly due to the presence of oxygen, which is the mostharmful factor with regard to the degradation of the polymer. Theoxidative degradation of polymers is amplified by the presence ofreducing chemical species such as iron and hydrogen sulphide. Thus,these different mechanisms lead to a partial degradation of the polymersand an inherent limitation to their effectiveness even before reachingthe zone to be treated. These various degradations therefore require anoverdose of polymer.

The treatment of subterranean formations often involves the use ofcross-linking agents. These are added to the polymer solutions, asdescribed in U.S. Pat. No. 4,683,949. The polymer/cross-linking agentmixture is then injected into the well to be treated with delayedgelation kinetics, the gel only setting after a few hours in theformation around the well. However, these methods are consideredunreliable and often use products classified as hazardous to theenvironment, made from chromium salts or resins. Moreover, gel-basedmethods do not make it possible to easily control either the gelationkinetics or the consistency of the gel; they generate a high risk ofdamage to the well, cause the retention and adsorption of thecross-linking agent in the reservoir rock, and only allow the gel to beplaced with difficulty in the high-permeability zones while preventingthe oil or gas zones from being invaded due to, inter alia, theviscosity which they confer on the injected fluid.

The problem that the applicant proposes to solve is that of protecting,against chemical and mechanical degradation, the polymers used in amethod for modifying the water permeability of a subterranean formation.

DISCLOSURE OF THE INVENTION

The invention relates to a method for modifying the water permeabilityof a subterranean formation using a (co)polymer capable of forming ahydrogel in the presence of water. To this end, the (co)polymer iscross-linked. In the context of the present invention, the (co)polymercan be cross-linked at the latest in the subterranean formation in orderto be able to modify the permeability of the latter. It is also possibleto prepare a composition comprising a (co)polymer that is cross-linkedprior to injecting the composition into the subterranean formation. Theinvention can therefore be implemented according to two differentembodiments.

According to a first embodiment, the invention relates to a method formodifying the water permeability of a subterranean formation comprisingat least the following steps:

-   -   Preparing an injection fluid from a dispersion of a hydrophilic        phase in a lipophilic phase, with water or brine, the dispersion        comprising:        -   a hydrophilic phase comprising at least one cross-linked            (co)polymer PR,        -   a lipophilic phase,        -   at least one interface polymer composed of at least one            monomer of formula (I):

-   -   in which,        -   R1, R2, R3 are independently selected from the group            comprising a hydrogen atom, a methyl group and Z—X,        -   Z is selected from the group comprising C(═O)—O; C(═O)—NH;            O—C(═O); NH—C(═O)—NH; NH—C(═O)—O; and a saturated or            unsaturated, substituted or unsubstituted carbon chain            having from 1 to 20 carbon atoms which may have one or more            heteroatoms selected from nitrogen and oxygen,        -   X is a group chosen from the alkanolamides, sorbitan esters,            ethoxylated sorbitan esters, glyceryl esters, and            polyglycosides; and comprising a saturated or unsaturated,            linear, branched or cyclic, optionally aromatic, hydrocarbon            chain,    -   Injecting the injection fluid into a subterranean formation,    -   said cross-linked (co)polymer PR forming a hydrogel in the        presence of water.

According to a second embodiment, the invention relates to a method formodifying the water permeability of a subterranean formation comprisingat least the following steps:

-   -   Preparing an injection fluid from a dispersion of a hydrophilic        phase in a lipophilic phase, with water or brine, the dispersion        comprising:        -   a hydrophilic phase comprising at least one non-cross-linked            (co)polymer NR,        -   a lipophilic phase,        -   at least one interface polymer composed of at least one            monomer of formula (I):

-   -   in which,        -   R1, R2, R3 are independently selected from the group            comprising a hydrogen atom, a methyl group and Z—X,        -   Z is selected from the group comprising C(═O)—O; C(═O)—NH;            O—C(═O); NH—C(═O)—NH; NH—C(═O)—O; and a saturated or            unsaturated, substituted or unsubstituted carbon chain            having from 1 to 20 carbon atoms which may have one or more            heteroatoms selected from nitrogen and oxygen,        -   X is a group chosen from the alkanolamides, sorbitan esters,            ethoxylated sorbitan esters, glyceryl esters, and            polyglycosides; and comprising a saturated or unsaturated,            linear, branched or cyclic, optionally aromatic, hydrocarbon            chain,    -   Injecting the injection fluid and a cross-linking agent for the        (co)polymer NR into a subterranean formation,    -   said (co)polymer NR, once cross-linked, forming a hydrogel in        the presence of water.

The expression “polymer composed of at least one monomer” means apolymer obtained from several molecules of at least one monomer. Thus, apolymer of one monomer corresponds to a polymer obtained from severalrepeating units of molecules of one monomer.

The Hydrophilic Phase in Lipophilic Phase Dispersion

The dispersion is a dispersion of a hydrophilic phase in a lipophilicphase. In other words, the lipophilic phase is the continuous phase andthe hydrophilic phase is the dispersed phase. The interface polymer ispositioned at the interface between the hydrophilic phase and thelipophilic phase. Preferably, the hydrophilic phase is an aqueous phaseand the lipophilic phase is an oil phase. Thus, the composition of theinvention is advantageously a water-in-oil dispersion, moreadvantageously a water-in-oil emulsion.

The interface polymer obtained by polymerization of at least one monomerof formula (I) forms a shell at the interface of the hydrophilic phaseand the lipophilic phase. In general, the shell is resistant tomechanical stresses such as shearing and more particularly shearing whenthe polymer is dissolved, when it is injected through valves, chokes andother restrictions at passage speeds greater than 3 meters per second,or when flushing a subterranean formation in the vicinity of thereservoir/borehole interface. The shell is also resistant to chemicalstresses which may result from the presence of oxygen, H₂S or metalsduring the injection phase. Preferentially, the shell is semi-permeable.

Preferably, as indicated above, the dispersion is basically in the formof an inverse emulsion.

In general, the hydrophilic phase is in the form of micrometric dropletsdispersed, and advantageously emulsified, in the lipophilic phase. Theaverage size of these droplets is advantageously between 0.01 and 30 m,and more advantageously between 0.05 and 3 m. The interface polymer istherefore positioned at the interface between the hydrophilic phase andthe lipophilic phase at each droplet. The average size of the dropletsis advantageously measured with a laser measuring apparatus usingconventional techniques which are part of the general knowledge of aperson skilled in the art. A Malvern Mastersizer device may be used forthis purpose.

Generally, the dispersion according to the invention contains between 10and 65% by weight of (co)polymer, and more advantageously between 30 and60% by weight.

Moreover, the dispersion according to the invention has a hydrophilicphase/lipophilic phase weight ratio advantageously between 0.1 and 100,more advantageously between 1 and 80, and even more advantageouslybetween 10 and 60.

The method for preparing the dispersion is described in the applicant'spatent application FR 3 075 219, cited as a reference.

The (Co)Polymer PR or NR in the Hydrophilic Phase

The (co)polymer present in the hydrophilic phase may be a natural(co)polymer, such as, for example, xanthan gums, guar gums,schizophyllan, scleroglucan or other compounds of the polysaccharidefamily, or a synthetic or semi-synthetic (co)polymer. Preferably, the(co)polymer is a synthetic (co)polymer.

When the (co)polymer is a synthetic (co)polymer, it is preferably a(co)polymer obtained from at least one non-ionic monomer and/or at leastone anionic monomer and/or at least one cationic monomer and/or azwitterionic monomer.

The non-ionic monomer or monomers that may be used in the context of theinvention may be chosen, in particular, from the group comprisingwater-soluble vinyl monomers. The non-ionic monomer does not comprisethe monomers of formula (I). Preferred monomers belonging to this classare, for example, acrylamide, methacrylamide, N-isopropylacrylamide,N,N-dimethylacrylamide, and N-methylolacrylamide. Also,N-vinylformamide, N-vinylacetamide, N-vinylpyridine andN-vinylpyrrolidone, acryloyl morpholine (ACMO), glycidyl methacrylate,glyceryl methacrylate and diacetone acrylamide may be used. A preferrednon-ionic monomer is acrylamide.

The anionic monomer or monomers are preferably selected from acrylicacid, methacrylic acid, itaconic acid, maleic acid, acrylamido tertiarybutyl sulphonic acid (also called ATBS or 2-acrylamido-2-methylpropanesulphonic acid), vinylsulphonic acid, vinylphosphonic acid, said anionicmonomer being unsalified, partially or totally salified, and salts of3-sulphopropyl methacrylate. The salified form advantageouslycorresponds to the salts of alkali metals (Li, Na, K, etc.), alkalineearth metals (Ca, Mg, etc.) or ammonium, in particular quaternaryammonium.

Hereinbefore and below, cationic monomers and anionic monomers, such as,for example, DMAEMA and ATBS, include unsalified and partially ortotally salified forms.

The cationic monomer or monomers that may be used in the context of theinvention may be chosen, in particular, from monomers of the acrylamide,acrylic, vinyl, allylic or maleic type having a quaternary ammoniumfunction by salification or quaternization. Mention may be made, inparticular and in a non-limiting manner, of quaternizeddimethylaminoethyl acrylate (DMAEA), quaternized dimethylaminoethylmethacrylate (DMAEMA), diallyldimethylammonium chloride (DADMAC),acrylamidopropyl trimethylammonium chloride (APTAC), and methacrylamidopropyltrimethyl ammonium chloride (MAPTAC).

The cationic monomer or monomers may also be chosen from associativecationic monomers as described in patent FR 2 868 783.

The monomer may optionally be a zwitterionic monomer of the acrylamide,acrylic, vinyl, allylic or maleic type having a quaternary amine orammonium function and a carboxylic, sulphonic or phosphoric acidfunction. Mention may be made, in particular and without limitation, ofdimethylaminoethyl acrylate derivatives, such as2-((2-(acryloyloxy)ethyl) dimethylammonio) ethane-1-sulphonate,3-((2-(acryloyloxy)ethyl) dimethylammonio) propane-1-sulphonate,4-((2-(acryloyloxy)ethyl) dimethylammonio) butane-1-sulphonate,[2-(acryloyloxy)ethyl] (dimethylammonio) acetate, dimethylaminoethylmethacrylate derivatives such as 2-((2-(methacryloyloxy) ethyl)dimethylammonio) ethane-1-sulphonate, 3-((2-(methacryloyloxy) ethyl)dimethylammonio) propane-1-sulphonate, 4-((2-(methacryloyloxy) ethyl)dimethylammonio) butane-1-sulphonate,[2-(methacryloyloxy)ethyl](dimethylammonio) acetate, dimethylaminopropylacrylamide derivatives such as 2-((3-acrylamidopropyl)dimethylammonio) ethane-1-sulphonate, 3-((3-acrylamidopropyl)dimethylammonio) propane-1-sulphonate, 4-((3-acrylamidopropyl)dimethylammonio) butane-1-sulphonate, [3-(acryloyloxy) propyl]dimethylammonio) acetate, dimethylamino propyl methylacrylamidederivatives, such as 2-((3-methacrylamidopropyl) dimethylammonio)ethane-1-sulphonate, 3-((3-methacrylamidopropyl) dimethylammonio)propane-1-sulphonate, 4-((3-methacrylamidopropyl) dimethylammonio)butane-1-sulphonate, and [3-(methacryloyloxy)propyl] (dimethylammonio)acetate.

According to one particular embodiment of the invention, the (co)polymeris composed solely of ATBS.

The (co)polymer is preferably an anionic (co)polymer made fromacrylamide, preferably an optionally partially post-hydrolyzed(co)polymer of acrylamide and acrylamido tertiary butyl sulphonic acid(ATBS), more preferably a ter(co)polymer of acrylamide, acrylic acid andacrylamido tertiary butyl sulphonic acid (ATBS).

The (co)polymer preferably contains between 10 mol % and 50 mol % ofanionic monomer(s), and more preferably between 20 mol % and 45 mol %.

The (co)polymer preferably contains between 50 mol % and 90 mol % ofnon-ionic monomer(s), and more preferably between 60 mol % and 75 mol %.

Preferably, the (co)polymer contains only anionic and non-ionic monomerunits. In other words, it is preferably obtained from at least oneanionic monomer and at least one non-ionic monomer.

The (co)polymer may be obtained by any polymerization technique such asconventional radical polymerization, controlled radical polymerization,also referred to as RAFT (reversible-addition fragmentation chaintransfer), NMP (nitroxide-mediated polymerization) or ATRP (atomtransfer radical polymerization).

According to the first embodiment of the invention, the (co)polymer ofthe hydrophilic phase is cross-linked, PR. In this case, it isadvantageously cross-linked by at least one cross-linking agent whichmay be chosen from the following groups:

-   -   polyethylenically unsaturated monomers (having at least two        unsaturated functions), such as, for example, vinyl, allyl,        acrylic and epoxy functions, for example        methylene-bis-acrylamide (MBA), triallyamine, or indeed, and/or    -   cross-linking agents made from multivalent metals such as salts        or complexes of Cr³⁺, Al³⁺, Fe³⁺ or Ti⁴⁺ and/or    -   macroinitiators such as polyperoxides, polyazos and transfer        polyagents such as polymercaptan (co)polymers, and polyols,        and/or    -   functionalized polysaccharides.

According to the first embodiment of the invention, the cross-linkingleading to the (co)polymer PR is advantageously carried out during orafter, and preferably during, the polymerization of the monomers.

According to the second embodiment of the invention, the cross-linkingof the (co)polymer NR is not carried out in the dispersion. In thiscase, it is the (co)polymer NR. The (co)polymer NR, which isnon-cross-linked, may be linear or branched.

Preferably, the (co)polymer NR is linear. However, in order to carry outthe invention, the (co)polymer NR is cross-linked once released directlyinto the injection fluid by means of at least one cross-linking agentwhich may be chosen from the above groups. This step is explained ingreater detail below in the paragraph “Permeability modificationmethod”.

The quantity of cross-linking agent in the (co)polymer NR or PRadvantageously lies in the range from 0.1 ppm to 50,000 ppm by weightrelative to the quantity of monomers, more advantageously in the rangefrom 1 ppm to 5,000 ppm, and even more advantageously in the range from10 ppm to 500 ppm.

Thus, this quantity of cross-linking agent is advantageously present inthe injection fluid when the (co)polymer NR is used.

According to another particular embodiment of the invention, the(co)polymer of the hydrophilic phase (PR or NR) comprises at least oneassociative cationic monomer and/or at least one LCST group.

In accordance with a particular embodiment, the (co)polymer may compriseat least one LCST group.

According to the general knowledge of a person skilled in the art, anLCST group corresponds to a group whose solubility in water, for a givenconcentration, is modified above a certain temperature and depending onthe salinity. It is a group having a heating transition temperaturedefining its lack of affinity with the solvent medium. Lack of affinitywith the solvent results in opacification or loss of transparency whichmay be due to precipitation, aggregation, gelation or viscosification ofthe medium. The minimum transition temperature is referred to as the“LCST” (lower critical solution temperature). For each LCST groupconcentration, a heating transition temperature is observed. This ishigher than the LCST, which is the minimum point of the curve. Belowthis temperature, the (co)polymer is soluble in water; above thistemperature, the (co)polymer loses its solubility in water.

In accordance with a particular embodiment, the (co)polymer may compriseat least one UCST group.

According to the general knowledge of a person skilled in the art, aUCST group corresponds to a group whose solubility in water, for a givenconcentration, is modified below a certain temperature and depending onthe salinity. It is a group having a cooling transition temperaturedefining its lack of affinity with the solvent medium. Lack of affinitywith the solvent results in opacification or loss of transparency whichmay be due to precipitation, aggregation, gelation or viscosification ofthe medium. The maximum transition temperature is called “UCST” (uppercritical solution temperature). For each UCST group concentration, acooling transition temperature is observed. This is lower than the UCST,which is the maximum point of the curve. Above this temperature, the(co)polymer is soluble in water; below this temperature, the (co)polymerloses its solubility in water.

In accordance with the invention, the (co)polymer has an advantageouslyhigh molecular weight. The expression “high molecular weight” denotesmolecular weights of at least 1 million g/mol, preferably between 2 and40 million g/mol, and more preferably between 5 and 30 million g/mol.The molecular weight is understood as weight average molecular weight.

The Interface Polymer

As already indicated, the interface polymer is obtained from at leastone monomer of formula (I):

-   -   in which,        -   R1, R2, R3 are independently selected from the group            comprising a hydrogen atom, a methyl group and Z—X,        -   Z is selected from the group comprising C(═O)—O; C(═O)—NH;            O—C(═O); NH—C(═O)—NH; NH—C(═O)—O; and a saturated or            unsaturated, substituted or unsubstituted carbon chain            having from 1 to 20 carbon atoms which may have one or more            heteroatoms selected from nitrogen and oxygen,        -   X is a group chosen from the alkanolamides, sorbitan esters,            ethoxylated sorbitan esters, glyceryl esters, and            polyglycosides; and comprising a saturated or unsaturated,            linear, branched or cyclic, optionally aromatic, hydrocarbon            chain.

In other words, X comprises a hydrocarbon chain and a group chosen fromalkanolamides, sorbitan esters, ethoxylated sorbitan esters, glycerylesters and polyglycosides. Advantageously, this hydrocarbon chaincomprises C₂ to C₃₀ carbon atoms. In a preferred embodiment, it is anintegral part of the group chosen from alkanolamides, sorbitan esters,ethoxylated sorbitan esters, glyceryl esters and polyglycosides.

X may therefore be one of the following groups:

-   -   an alkanolamide, preferably of the formula diethanolamide        monooleate (Witcamide 511), stearoyl ethanolamide (Witcamide        70), oleic acid monoisopropanolamide (Witcamide 61), isostearic        acid monoisopropanolamide (Witcamide SPA), coconut        monoisopropanolamide (Empilan CIS), coconut monoethanolamide,        oleic acid diethanolamide (Mexanyl), oleyl monoisopropanolamide        (Simaline IE 101),    -   a sorbitan ester, for example, but not limited to, sorbitan        monolaurate (Span 20), sorbitan monopalmitate (Span 40),        sorbitan monostearate (Span 60), sorbitan monoisostearate (Span        70), sorbitan tristearate (Span 65), sorbitan monooleate (Span        80), sorbitan sesquioleate (Span 83) or sorbitan trioleate (Span        85),    -   an ethoxylated sorbitan ester, preferably of the formula        polyethylene glycol sorbitan monolaurate (Tween 20),        polyethylene glycol sorbitan monopalmitate (Tween 40),        polyethylene glycol sorbitan monostearate (Tween 60),        polyethylene glycol sorbitan monooleate (Tween 80) or        polyethylene glycol sorbitan trioleate (Tween 85),    -   a glyceryl ester, preferably of the formula polyglycerol        monolaurate (Decaglyn 1-L), polyglycerol myristate (Decaglyn        1-M), polyglycerol decaoleate (Polyaldo 10-10-0), polyglycerol        distearate (Polyaldo 6-2-S), polyglycerol oleate (Polyaldo        10-1-0), polyglycerol caprate (Polyaldo 10-1 CC KFG), or        polyglycerol stearate (Polyaldo 10-1-S),    -   a polyglucoside, preferably of the formula decyl glucoside        (Triton BG-10), lauryl glucoside (Plantacare 1200UP), capryl        glucoside (Plantacare 810 UP), butyl glucoside (Simulsol SL 4),        heptyl glucoside (Simulsol SL 7 G), octyl and decyl glucoside        (Simulsol SL 8), decyl glucoside (Simulsol SL 10), undecyl        glucoside (Simulsol SL 11 W), decyl and hexadecyl glucoside        (Simulsol SL 26), or octyl and hexadecyl glucoside (Simulsol SL        826).

According to one particular embodiment, the monomer of formula (I) hasan HLB value advantageously lower than 4.5, and advantageously of atleast 1.

The HLB value (hydrophilic-lipophilic balance) makes it possible toquantify the balance that exists between the hydrophilic part and thelipophilic part of a molecule. This value is determined by calculatingthe values of the different parts of the molecule, as described byGriffin in 1949 (Griffin W C, Classification of Surface-Active Agents byHLB, Journal of the Society of Cosmetic Chemists 1 (1949): 311).

In the present invention, the Griffin method, conventionally used, isbased on calculating the values of the chemical groups of the molecule.Griffin assigned a value of between 0 and 20, thus giving information onthe solubility of the molecule in a hydrophilic medium and in alipophilic medium. Thus, substances having an HLB of 10 are distributedequally in the two phases, i.e., the hydrophilic part in the hydrophilicphase and the hydrophobic part in the lipophilic phase.

HLB=20 (Mh/M)

-   -   M: the molecular weight of the molecule    -   Mh: the molecular weight of the hydrophilic part.

In a preferred embodiment, the monomer of formula (I) has the followingformula:

-   -   in which,        -   R1, R2, R3, independently, are a hydrogen atom or a methyl            group,        -   Z is selected from the group comprising CH₂, C(═O)—O,            C(═O)—NH, and —(C═O)—O—CH₂—CH(OH)—CH₂,        -   X is a group chosen from the alkanolamides and the sorbitan            esters, and comprising a saturated or unsaturated, linear,            branched or cyclic, optionally aromatic, hydrocarbon chain.

In accordance with a preferred embodiment, the monomer of formula (I) isselected from sorbitan monooleate (meth)acrylate, 2-hydroxypropyl(meth)acrylate of diethanolamide monooleate and sorbitan monooleateglyceryl (meth)acrylate.

In accordance with a preferred embodiment, the monomer of formula (I) isas follows:

This preferred monomer corresponds to the formulaH₃C—(CH₂)₇—CH═CH—(CH₂)₇—C(═O)—N(CH₂CH₂OH)—(CH₂)₂O—CH₂—CH(OH)—CH₂—O—C(═O)—C(CH₃)═CH₂.

In a particular embodiment of the invention, the interface polymeraccording to the invention is obtained by polymerization of at least onemonomer of formula (I).

In a particular embodiment, the interface polymer according to theinvention is obtained by polymerization of at least one monomer offormula (I) and at least one non-ionic monomer and/or at least oneanionic monomer and/or at least one cationic monomer.

The various monomers that are implemented may be chosen from among therespective lists mentioned above in the description of the (co)polymerof the hydrophilic phase (PR or NR).

Advantageously, the interface polymer comprises between 0.0001 and 10%,more advantageously between 0.0001 and 5%, and even more advantageouslybetween 0.0001 and 1% of the monomer of formula (I), by weight relativeto the total weight of monomers.

In general, the time required to degrade the shell increases with thepercentage of monomer of formula (I).

Where appropriate, the interface polymer comprises between 50 and99.9999%, and more advantageously between 60 and 99.9999% of non-ionicmonomer (different from the monomer of formula (I)) by weight relativeto the total weight of monomers.

Where appropriate, the interface polymer comprises between 10 and99.9999%, and more advantageously between 20 and 99.9999% of anionicmonomer, by weight relative to the total weight of monomers.

Where appropriate, the interface polymer comprises between 1 and99.9999%, and more advantageously between 10 and 99.9999% of cationicmonomer, by weight relative to the total weight of monomers.

Advantageously, the interface polymer is neither cross-linked norbranched. It is advantageously linear.

The Shell

According to the invention, the interface polymer forms a shell arounddroplets forming the hydrophilic phase. In addition to the monomersmentioned above, the interface polymer may comprise at least onestructural agent. The structural agent is advantageously chosen fromdiacrylamides or methacrylamides of diamines; acrylic esters of di-,tri- or tetrahydroxy compounds; methacrylic esters of di-, tri- ortetrahydroxy compounds; divinyl compounds preferably separated by an azogroup; diallyl compounds preferably separated by an azo group; vinylesters of di- or trifunctional acids; allyl esters of di- ortrifunctional acids; methylenebisacrylamide; diallylamine;triallylamine; tetraallylammonium chloride; divinylsulphone;polyethylene glycol dimethacrylate and diethylene glycol diallyl ether.

Permeability Modification Method

The injection fluid used in the method according to the invention hasthe functionality of gelling in high-permeability and/or highwater-content zones in order to reduce or eliminate the permeability ofthese zones.

Whatever the form used (a dispersion, a concentrated dispersion or asolid form obtained from the dispersion), the protective effect of theshell is produced and the (co)polymers PR and NR are thus protected fromchemical and mechanical degradation, in particular during injection.

In other words, and more precisely, the method for modifying the waterpermeability of a subterranean formation according to the inventioncomprises the following steps:

-   -   Preparing an aqueous injection fluid by adding, to water or        brine, the dispersion a hydrophilic phase in a lipophilic phase        as described above, or its concentrated form after removal of        part of the water, or its solid form obtained after drying of        said dispersion,    -   Injecting the injection fluid into a subterranean formation,    -   Releasing said (co)polymer PR or NR by hydrolysis of the        interface polymer,    -   Modifying the water permeability of the subterranean formation        by gelation of said injection fluid.

The operations of modifying the water permeability of a reservoir differfrom enhanced oil recovery techniques. The modification operations arecharacterized by volume-limited injections of polymer solution in orderto create a localized phenomenon in the reservoir, namely, forconformance, blocking of the high-permeability zones and, for stoppingwater, blocking of zones where water enters the formation. Injectionsare generally carried out either via an injection well or via aproduction well over fairly short periods of a few days and generallyless than one month, and with volumes representing less than 5% of thepore volume of the reservoir. The pore volume corresponds to the volumenot occupied by rock in the reservoir, which allows a correlation withthe permeable zone.

Conversely, polymer-based enhanced oil recovery techniques involve thecontinuous and prolonged injection of polymer solution to flush thereservoir from an injection well to a production well. The objective isnot to treat a zone of the reservoir but the reservoir as a whole, inorder to recover the maximum amount of oil. For this purpose, it isnecessary to inject a much larger volume of aqueous solution generallyrepresenting at least 50% to 500%, or even more, of the pore volume. Anoily and sometimes gaseous aqueous mixture is then recovered from theproduction wells.

As already indicated, the (co)polymer PR is in cross-linked form inorder to be able to modify the permeability of the subterraneanformation, the (co)polymer PR forming a hydrogel in the presence ofwater. In other words, when it is released from the shell, the(co)polymer PR swells by taking up water. By swelling, the (co)polymerPR causes the injection fluid to gel, thereby forming a hydrogel. Thegelation of the injection fluid results in the blocking of certain zonesand consequently the modification of the permeability of thesubterranean formation.

As already indicated, the (co)polymer NR is not in cross-linked formwhen the injection fluid is injected. Once released from the shell, the(co)polymer NR cross-links, with the aid of a cross-linking agent,forming a hydrogel in the presence of water. In other words, when it isin cross-linked form, the (co)polymer NR swells by taking up water. Byswelling, the cross-linked (co)polymer NR causes the injection fluid togel, thereby forming a hydrogel. The gelation of the injection fluidresults in the blocking of certain zones and consequently themodification of the permeability of the subterranean formation.

As previously mentioned, the dispersion as described above makes itpossible not only to protect the (co)polymers PR and NR from chemicaland mechanical degradation during the steps of preparing and injectingthe injection fluid, but also to delay the gelation of the fluid. Theseproperties are obtained by virtue of the shell formed by the interfacepolymer which, when degraded by hydrolysis, leads to the release of the(co)polymer PR or NR.

According to the second embodiment of the invention, in which the(co)polymer NR is subjected to a cross-linking step after its releasefrom the dispersion, the injection fluid comprises at least onecross-linking agent which can be chosen from the cross-linking agentsmentioned above, in particular cross-linking agents made frommultivalent metals such as salts or complexes of Cr³⁺, Al³⁺, Fe³⁺ orTi⁴⁺. In this particular embodiment, once the (co)polymer has beenreleased, it reacts with the cross-linking agent present in theinjection fluid to form a gel. According to this embodiment, the(co)polymer of the hydrophilic phase is generally not cross-linkedbefore it is released.

In a particular embodiment of the first embodiment of the invention, across-linking agent as described above can also be injected with theinjection fluid even if the (co)polymer PR is already cross-linked.Indeed, depending on the characteristics of the subterranean formation,it may be advantageous to cross-link the (co)polymer PR more strongly.

According to the invention (PR or NR, depending on the embodiment), theinjection fluid advantageously comprises between 30 ppm and 50,000 ppm(by weight) of the dispersion or concentrated dispersion or solid formobtained from the dispersion, more advantageously between 100 and 30,000ppm, and even more advantageously between 300 and 15,000 ppm.

According to the invention, the injection fluid advantageously comprisesbetween 10 ppm and 15,000 ppm (by weight) of (co)polymer (PR or NRaccording to the embodiment), more advantageously between 50 and 10,000ppm, and even more advantageously between 100 and 5,000 ppm.

Once the injection fluid is injected, the (co)polymer is releasedfollowing degradation of the shell formed by the interface polymer underthe temperature and/or pH conditions of the subterranean formation.

Thus, the (co)polymer included in the hydrophilic phase is protected bythe shell formed from at least one interface polymer obtained bypolymerization of at least one monomer of formula (I), the shell beingcapable of being degraded under the temperature and/or pH conditions ofthe subterranean formation.

The method according to the invention makes it possible to protect thepolymer from mechanical and chemical degradation (oxygen, metals, H₂S)linked to the preparation of the composition injected with the polymer,and to its injection, while maintaining good injectivity and a goodability to block the permeable zones of the subterranean formation. Inaddition, the shell makes it possible to delay the release of the(co)polymers.

Without wishing to be bound to any theory, the formation of theinjection fluid by introducing the dispersion according to the inventiondoes not make it possible to release the (co)polymer from its shell,even in the presence of a reverser (oil-in-water surfactant). The pHand/or temperature of the subterranean formation allows hydrolysis ofthe interface polymer and thus the delayed release of the (co)polymer.

The invention and the advantages resulting from it appear more clearlyfrom the following figures and examples that are given to illustrate theinvention and in non-limiting manner.

DESCRIPTION OF THE FIGURES Examples of Embodiments of the InventionExample 1

Part A: Preparation of a Composition C1 Comprising a Monomer X1Corresponding to formula (I)

0.16 g of glycidyl methacrylate (97% by weight aqueous solution) isadded to 20.0 g of oleyl diethanolamide (diethanolamide monooleateWitcamide 511-AkzoNobel) with magnetic stirring. The medium is stirredfor 12 hours at ambient temperature.

Part B: Preparation of a Dispersion with an Interface Polymer(Invention)

A hydrophilic phase is prepared containing 365.8 g of acrylamide (50% byweight aqueous solution), 24.6 g of acrylic acid (100%), 234.6 g ofsodium salt of 2-acrylamido-2-tert-butylsulphonic acid (50% by weightaqueous solution), 29.0 g of deionized water, 25.9 g of sodium hydroxide(50% by weight aqueous solution), 0.5 g of methylenebisacrylamide, 1.6 gof an aqueous solution of sodium hypophosphite (5 g/L), 0.94 g oftert-butyl hydroperoxide (0.7% by weight aqueous solution), 0.40 g ofpentasodium salt of diethylenetriaminepentaacetic acid (Versenex 80)dispersed in a mixture of 280 g of aliphatic hydrocarbon D100S (ExxsolD100) and 20 g of composition C1 comprising a monomer X1 of part A. ThepH is adjusted to 6.50.

After homogenization and deoxygenation with nitrogen for 30 minutes,polymerization is initiated by adding a sodium bisulphite solution.

Example 2

Part A: Preparation of a Composition C2 Comprising a Monomer X2Corresponding to Formula (I)

15.7 g of glycidyl methacrylate (97% by weight aqueous solution) isadded dropwise to 20.0 g of oleyl diethanolamide (diethanolamidemonooleate Witcamide 511-AkzoNobel) with magnetic stirring. The mediumis stirred for 12 hours at ambient temperature.

Part B: Preparation of a Dispersion without Interface Polymer(Counter-Example)

A hydrophilic phase is prepared containing 365.8 g of acrylamide (50% byweight aqueous solution), 24.6 g of acrylic acid (100%), 234.6 g ofsodium salt of 2-acrylamido-2-tert-butylsulphonic acid (50% by weightaqueous solution), 29.0 g of deionized water, 25.9 g of sodium hydroxide(50% by weight aqueous solution), 0.5 g of methylenebisacrylamide, 1.6 gof an aqueous solution of sodium hypophosphite (5 g/L), 0.94 g oftert-butyl hydroperoxide (0.7% by weight aqueous solution), 0.40 g ofpentasodium salt of diethylenetriaminepentaacetic acid (Versenex 80)dispersed in a mixture of 280 g of aliphatic hydrocarbon D100S (ExxsolD100) and 20 g of oleyl diethanolamide (diethanolamide monooleateWitcamide 511-AkzoNobel). The pH is adjusted to 6.50.

After homogenization and deoxygenation with nitrogen for 30 minutes,polymerization is initiated by adding a sodium bisulphite solution.

Part C: Preparation of a Dispersion with an Interface Polymer from aDispersion without an Interface Polymer (Invention)

36 g of acrylamide (50% by weight aqueous solution), 1.6 g of tert-butylhydroperoxide (0.7% by weight aqueous solution) and 0.6 g of compositionC2 comprising a monomer X2 are added to the dispersion obtained in partB. The formation of the interface polymer, by polymerization of themonomers of composition C2, is initiated by adding a sodium bisulphitesolution (radical initiator).

Resistance to Mechanical Degradation

In order to demonstrate the mechanical protection of the polymerprovided by the shell, aqueous solutions containing 1000 ppm of thepolymer of example 1 (with shell) and of the counter-example (withoutshell—example 2, part B) were prepared in synthetic seawater. Thesolutions were sheared by passing them through a pipe with a smallcross-section at different pressures. The shear gradient was determinedby measuring the flow at the outlet of a 0.5 mm capillary. The sampleswere then collected at the outlet of the pipe and the viscosity wasmeasured at 7.3 s⁻¹ and 25° C. on a Kinexus pro+by Malvern Instruments.

The data is displayed in Table 1. The polymer with no shell is rapidlydegraded. Polymer solutions that have a shell maintain constantviscosities very close to 1.0 cp (1 cp=1 cps=1 mPa·s). The solutionsprepared according to the invention were collected after shearing, i.e.,at each measurement point. After measuring their viscosity, they werethen activated by being placed for 4 days in an oven at 60° C. Theirviscosity after the release of the water-soluble polymer was thenmeasured. The latter remains very close to the viscosity of thenon-sheared solutions without an initial shell (counter-example).

TABLE 1 Viscosity (cp) of the polymer solution measured at 7.3 s⁻¹ and T= 25° C. as a function of the previously applied shear. Shear gradient(s⁻¹) 0 50,000 100,000 148,000 210,000 Counter-example: 8.1 6.5 5.1 4.23.3 viscosity without shell Example 1: 1.1 1.0 1.0 1.0 1.0 viscositywith shell Example 1: 8.0 8.1 8.1 7.9 8.0 viscosity after degradation ofthe shell

1. A method for modifying water permeability of a subterraneanformation, comprising at least the following steps: preparing aninjection fluid from a dispersion of a hydrophilic phase in a lipophilicphase, with water or brine, the dispersion comprising: a hydrophilicphase comprising at least one non-cross-linked (co)polymer NR, alipophilic phase, at least one interface polymer composed of at leastone monomer of formula (I):

in which, R1, R2, R3 are independently selected from the groupconsisting of a hydrogen atom, a methyl group and Z—X, Z is selectedfrom the group consisting of C(═O)—O; C(═O)—NH; O—C(═O); NH—C(═O)—NH;NH—C(═O)—O; and a saturated or unsaturated, substituted or unsubstitutedcarbon chain having from 1 to 20 carbon atoms which may have one or moreheteroatoms selected from nitrogen and oxygen, X is a group chosen fromalkanolamides, sorbitan esters, ethoxylated sorbitan esters, glycerylesters, and polyglycosides; and comprising a saturated or unsaturated,linear, branched or cyclic, optionally aromatic, hydrocarbon chain,injecting the injection fluid and a cross-linking agent for the(co)polymer NR into a subterranean formation, said (co)polymer NR, oncecross-linked, forming a hydrogel in the presence of water.
 2. The methodaccording to claim 1, wherein the (co)polymer NR is obtained from atleast one non-ionic monomer and/or at least one anionic monomer and/orat least one cationic monomer and/or at least one zwitterionic monomer.3. The method according to claim 2, wherein the non-ionic monomer isselected from the group consisting of acrylamide, methacrylamide,N-isopropylacrylamide, N,N-dimethylacrylamide, N-methylolacrylamide,N-vinylformamide, N-vinylacetamide, N-vinylpyridine, N-vinylpyrrolidone,acryloyl morpholine, glycidyl methacrylate, glyceryl methacrylate anddiacetone acrylamide.
 4. The method according to claim 2, wherein theanionic monomer is chosen from the group consisting of salts of3-sulphopropyl methacrylate, and unsalified, partially or totallysalified monomers chosen from acrylic acid, methacrylic acid, itaconicacid, maleic acid, acrylamido tertiary butyl sulphonic acid,vinylsulphonic acid, and vinylphosphonic acid.
 5. The method accordingto claim 1, wherein the interface polymer comprises, in addition to themonomer of formula (I), at least one non-ionic monomer and/or at leastone anionic monomer and/or at least one cationic monomer.
 6. The methodaccording to claim 1, wherein the monomer of formula (I) has thefollowing formula:

in which, R1, R2, R3, independently, are a hydrogen atom or a methylgroup, Z is selected from the group consisting of CH₂, C(═O)—O,C(═O)—NH, and —(C═O)—O—CH₂—CH(OH)—CH₂, X is a group chosen fromalkanolamides and sorbitan esters, and comprising a saturated orunsaturated, linear, branched or cyclic, optionally aromatic,hydrocarbon chain.
 7. The method according to claim 1, wherein themonomer of formula (I) is selected from sorbitan monooleate(meth)acrylate, 2-hydroxypropyl (meth)acrylate of diethanolamidemonooleate or sorbitan monooleate glyceryl (meth)acrylate.
 8. The methodaccording to claim 1, wherein the monomer of formula (I) has thefollowing formula:


9. The method according to claim 1, wherein the (co)polymer comprises atleast one associative cationic monomer and/or at least one LCST group.10. The method according to claim 2, wherein the monomer of formula (I)is selected from sorbitan monooleate (meth)acrylate, 2-hydroxypropyl(meth)acrylate of diethanolamide monooleate or sorbitan monooleateglyceryl (meth)acrylate.
 11. The method according to claim 8, whereinthe (co)polymer NR is obtained from at least one non-ionic monomerand/or at least one anionic monomer and/or at least one cationic monomerand/or at least one zwitterionic monomer, and wherein: the non-ionicmonomer is selected from the group consisting of acrylamide,methacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide,N-methylolacrylamide, N-vinylformamide, N-vinylacetamide,N-vinylpyridine, N-vinylpyrrolidone, acryloyl morpholine, glycidylmethacrylate, glyceryl methacrylate and diacetone acrylamide; and theanionic monomer is chosen from the group consisting of salts of3-sulphopropyl methacrylate, and unsalified, partially or totallysalified monomers chosen from acrylic acid, methacrylic acid, itaconicacid, maleic acid, acrylamido tertiary butyl sulphonic acid,vinylsulphonic acid, and vinylphosphonic acid.